This invention relates to lighting systems and, more particularly, to lighting systems that use light emitting diodes (LEDs).
LEDs are increasingly being used in lighting/illumination applications, such as traffic signals, color wall wash lighting, backlights, displays and general illumination, with one ultimate goal being a replacement for the ubiquitous incandescent light bulb. In order to provide a broad spectrum light source, such as a white light source, from a relatively narrow spectrum light source, such as an LED, the relatively narrow spectrum of the LED may be shifted and/or spread in wavelength.
For example, a white LED may be formed by coating a blue emitting LED with an encapsulant material, such as a resin or silicon, that includes therein a wavelength conversion material, such as a YAG:Ce phosphor, that emits yellow light in response to stimulation with blue light. Some, but not all, of the blue light that is emitted by the LED is absorbed by the phosphor, causing the phosphor to emit yellow light. The blue light emitted by the LED that is not absorbed by the phosphor combines with the yellow light emitted by the phosphor, to produce light that is perceived as white by an observer. Other combinations also may be used. For example, a red emitting phosphor can be mixed with the yellow phosphor to produce light having better color temperature and/or better color rendering properties. Alternatively, one or more red LEDs may be used to supplement the light emitted by the yellow phosphor-coated blue LED. In other alternatives, separate red, green and blue LEDs may be used. Moreover, infrared (IR) or ultraviolet (UV) LEDs may be used. Finally, any or all of these combinations may be used to produce colors other than white.
LEDs also may be energy efficient, so as to satisfy ENERGY STAR® program requirements. ENERGY STAR program requirements for LEDs are defined in “ENERGY STAR® Program Requirements for Solid State Lighting Luminaires, Eligibility Criteria—Version 1.1”, Final: Dec. 19, 2008, the disclosure of which is hereby incorporated herein by reference in its entirety as if set forth fully herein.
In order to encourage development and deployment of highly energy efficient solid state lighting (SSL) products to replace several of the most common lighting products currently used in the United States, including 60-watt A19 incandescent and PAR 38 halogen incandescent lamps, the Bright Tomorrow Lighting Competition (L Prize™) has been authorized in the Energy Independence and Security Act of 2007 (EISA). The L Prize is described in “Bright Tomorrow Lighting Competition (L Prize™)”, May 28, 2008, Document No. 08NT006643, the disclosure of which is hereby incorporated herein by reference in its entirety as if set forth fully herein. The L Prize winner must conform to many product requirements including light output, wattage, color rendering index, correlated color temperature, dimensions and base type.